Stiffness reduction factor ( t ) due to column inelasticity:

a).  P_f / P_y <= 0.5 (elastic):     t =1.0
b).  P_f / P_y > 0.5 (inelastic):    t = 4 (P_f / P_y). ( 1 - P_f / P_y)

  P_y = F_y.A_g
  P_f - factored axial load on the column, P_f <= 0.85 P_y

Direct Analysis:

  1). Use any second-order elastic analysis

  2). Consider notional load for out-of-plumbness (0.2% of total gravity load)

  3). Use a reduced flexural and axial stiffness to account for influence of inelasticity (EI^* = 0.8 t EI, EA^* = 0.8 EA)

  4). K = 1.0

Effective Length Method: (B₂ = D_2nd-order / D_1st-order <= 1.5)

  1). Use any second-order elastic analysis (nominal geometry, stiffness)

  2). Consider notional load for out-of-plumbness (0.2% of total gravity load)

  3). Determine K from a sideway buckling analysis